PROJECT SUMMARY Rheumatoid arthritis (RA) affects 1% of the adult world population, including 1.5 million adults in the U.S., and contributes significantly to the global burden of disease. There is currently no cure for RA, and available medications are often associated with risks of toxicity and adverse events. However, pregnancy is known to have remarkable disease modifying properties on RA, inducing a natural amelioration in 50-75% of patients, the mechanism(s) of which remain unknown. Our goal in this proposal is to gain an understanding of the mechanism(s) underlying the natural amelioration of RA during pregnancy so that, in the long-term, novel therapy can be developed to mimic the beneficial effect of pregnancy on RA outside the context of pregnancy, to alleviate RA symptoms in both women and men. We hypothesize that the biological processes that lead to the natural improvement of RA during pregnancy are reflected in pregnancy-induced changes in gene expression at the systemic level. We previously established a unique prospective pregnancy cohort of RA and healthy women, with samples collected before, during and after pregnancy for gene expression studies. We now propose to examine changes in gene expression that occur during pregnancy in RA and healthy women in a larger sample of this cohort in order to gain an understanding of potential mechanism(s) whereby pregnancy naturally modulates disease activity in RA. The proposal is divided into 3 aims. In aim 1, a set of candidate genes with expression patterns that are associated with improvement in RA disease activity will be investigated. In aim 2, gene expression signatures associated with RA will be examined before pregnancy and the influence of pregnancy-induced expression changes on the RA signature will be investigated. In aim 3, pregnancy-induced gene expression patterns in RA and healthy women will be examined to provide insight into normal biological changes that occur during pregnancy, and how these may be altered in RA. In all 3 aims, potential epigenetic mechanisms that may be regulating expression during pregnancy will be investigated to provide insight into the natural amelioration of RA during pregnancy, and into why some women do not improve during pregnancy, but worsen. The proposed innovative approach includes a) a unique prospective pregnancy cohort which includes pre-pregnancy as baseline, b) a successful recruitment approach, c) a powerful longitudinal study design, d) state-of-the-art RNA sequencing technology and bioinformatics methods to assess gene expression, e) powerful statistical analysis approaches, and f) epigenetic studies to examine regulation of candidate gene expression. Such investigations using the proposed approach are novel in the context of both normal and RA pregnancies. There is a high potential that the findings can lead to identification of novel drug targets for improved RA therapy without side effects of current medications, and novel biomarkers of RA disease activity.